Photochemical Skeletal Editing: One-Step Transformation of Diaryl Dithiophenes into Regiodefined Helicenes

Abstract

Skeletal editing is reshaping synthetic design form the direct, atom-level manipulation of molecular frameworks. While single-atom insertion or deletion has been achieved in simple aromatic systems, strategies for editing S-heterocycles within complex, functional molecules remain underdeveloped due to the inertness of C-S bonds and the lack of mild, direct methods to reconstruct the entire aromatic skeleton. We report a photochemical skeletal editing approach that directly converts readily available diaryl dithiophenes into regiodefined π‑extended helicenes, bypassing multistep sequences and regioselectivity limitations of classical syntheses. This transformation constitutes the formation of two benzene rings and a ring opening of thiophene through a cascade-initiated steps under light. The process involves regioselective photocyclization, followed by C-S bond cleavage, a second annulation and desulfurization, all occurring in one-pot synthetic operation. The reaction proceeds under mild conditions, displays broad substrate scope, and enables the efficient regioselective synthesis of diverse benzo-fused helicenes. The resulting π-extended helicenes exhibit good photophysical and chiroptical properties. Their performance of circularly polarized luminescence (CPL) shows the attractive luminescence dissymmetry factors (|g_lum|) reaching magnitudes on the order of 10^-3.